A Low-Profile Dual-Polarized Frequency-Selective Rasorber Based on One-Eighth Wavelength Spacer and Interdigital Resonator

This paper presents a low-profile dual-polarized frequency-selective rasorber (FSR) that combines the design of a resistive absorber frequency-selective surface (FSS) with a bandpass FSS to achieve two absorption bands located on both sides of a transmission band. The main contribution of this research is the optimization of the thickness of the air spacer between the two dielectric substrates, achieved with the aid of the Advanced Design System software. This optimization was performed to achieve a thickness equivalent to one-eighth of the wavelength at the central frequency of the passband (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>), which is half the standard value typically used, in order to obtain a low-profile structure with a wide absorption band. A theoretical analysis, based on transmission line theory, validated the λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/8 choice. Both FSSs feature new geometries, where the lossy FSS elements are split-rings with lumped resistors and interdigital resonators inserted to ensure a parallel resonance. The proposed FSR exhibits an operating bandwidth of 120%(fractional bandwidth) from 4.03 to 16.12 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GHz</i> (|S11| < −10 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dB</i>) and a passband centered at 9.7 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GHz</i> with a minimum insertion loss of 1.0 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dB</i>, under normal incidence. Due to the low-profile characteristic and the reduced physical dimensions of the unit cell relative to the λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub>, where λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> is the free-space wavelength at the lowest operating frequency, the presented FSR has good angular stability up to 40° angle of incidence. An equivalent circuit model is presented to provide physical insight of the structure’s behavior. A prototype was fabricated and tested to validate the design approach and prove the proposed concept. Good agreement was observed between the experimental and simulated results.